1. Field of the Invention
This invention relates to a granulating and coating technique, and more particularly to a technique wherein a powdery and/or granular material is placed in a rotary drum and then the drum is rotated about a substantially horizontal shaft so as to perform granulating and coating of the powdery and/or granular material.
2. Description of the Related Art
As a granulating and coating technique of the type described, there has been known a technique wherein a rotary drum, called also a coating pan, is rotated about a horizontal shaft and a gas such as hot air is fed into the rotary drum and discharged therefrom, whereby a powdery and/or granular material, such as pharmaceuticals, food products, chemical products and other various materials, is granulated and/or coated within the rotary drum.
In the granulating and coating apparatus of the type described, in order to feed a coating liquid and/or a binder liquid to articles to be coated contained in the rotary drum, i.e. the powdery or granular material, a nozzle unit constituted by a spray nozzle is inserted therein.
Now, with the ordinary construction, the nozzle unit is extended through a hot air supply passage into the rotary drum, whereby the coating liquid and the like in the nozzle unit is heated by the hot air and hardened finally, so that smooth liquid supply may become impossible.
Then, to obviate this problem, among granulating and coating apparatuses of the type IDA.X (IDA. 500. 750. 1000. .times..) manufactured and marketed by Dumoulin Co. of France, there are apparatuses wherein a gas blow-out tube is provided at an axial portion of a rotary drum, the direction of gas blow-out being fixed.
However, the inventors of the present invention have found out problems with this fixed-type gas blowout tube. Namely, as the direction of the blow-out gas from the tube is constant, it is impossible to variably adjust the direction and the flow rate of the blow-out gas depending on the properties of the coating liquid and the types of the products to be coated. Thus, the intended effects cannot necessarily be achieved.
For example, an aqueous type coating liquid varies between one using an aqueous solution of water-soluble substance such as hydroxipropylcellulose or hydroxipropylmethylcellulose; one using an emulsion such as Eudragit; and one using a suspension in which very small powder of carboxymethylethylcellulose (CMEC) or hydroxypropylmethylcellulose acetate succinate (AQOAT) is suspended in an aqueous solvent medium. There are large differences in film-making properties in these substances. And, when a main component to be coated is easily water-soluble, it is necessary to perform drying quicker than main component which is not easily water-soluble. With the gas blow out tube in which the gas blow-out direction is fixed, the drying process is always same, so that the various requirements as described above cannot be met.
Further, the present inventors have also found that, in the case of the aqueous type coating using a dispersion such as an emulsion or a suspension, a high quality product can be obtained when granulating and coating are carried out while the gas is blown out to the rear in the rotating direction of the rotary drum relative to the nozzle unit for feeding the coating liquid.
It is an object of the present invention to provide a granulation coating technique being widely compatible with the characteristic properties of the coating liquids and the products to be coated and capable of obtaining a high quality product.
It is another object of the present invention to provide a granulation coating technique capable of obtaining a high quality product even when the gas blow-out direction is fixed.
The above described objects, other objects and novel characteristics of the present invention will become clear from description of the present specification and the accompanying drawings.